It is common practice in many medical procedures, such as percutaneous transluminal angioplasty, to insert a guidewire, catheter, or other elongated instrument through a tubular catheter introducer that has been placed in the vasculature of a patient. The catheter introducer has a housing at its proximal end that has a self-sealing port through which the elongated instruments may be inserted, manipulated and removed. The seal typically is formed by a self-sealing valve through which the instrument is passed.
U.S. Pat. No. 4,430,081 to Timmermans describes a catheter introducer having a tubular shaft, a housing and a self-sealing, three-part, hemostatic flapper-type valve contained in the housing. The three-part valve has three disc-like elements sandwiched together including a first proximal disc having a slit, a second disc having a through-hole, and a third distal disc having a central flexible flap that overlies the hole. The first and second discs are said to effect a seal when an elongate device is passed through the valve. The third, distal disc cooperates with the second disc to effect a seal in the absence of an instrument passing through the device. In the latter mode, the device relies upon the patient's blood pressure to urge the flap of the third valve element against the hole in the middle disc. The effectiveness of the seal therefore depends in part on the fluid pressure within the housing, including the patient's blood pressure.
It often is desirable to aspirate a sample of the patient's blood through the introducer. For that purpose, a side port is provided on the housing distally of the valve. When the valve includes a flapper element, aspiration tends to draw the flap distally, away from the hole of the second valve element and potentially disrupting the seal. Air consequently could be drawn into the blood vessel, presenting risk of an air embolism. Blood leakage also could occur. Additionally, fluctuations in a patient's blood pressure similarly can cause variations in the effectiveness of the seal.
It is important that when a flapper-type of hemostatic valve is used the valve maintain its seal over a relatively wide range of pressures, including those reduced pressures that result from aspiration applied through the side port as well as fluctuations in a patient's blood pressure. It is therefore among the general objects of the invention to provide catheter introducers having an improved flapper-type of hemostatic valve that more effectively seals the lumen of the introducer over a wider range of pressures.
Also among the desirable features of a hemostatic catheter introducer is that the hemostatic valve should present as little drag as possible to an instrument passed through the introducer. In many procedures, it can be expected that the physician will rely on tactile feedback of the catheter when manipulating the catheter into a desired position. It is desirable to minimize the drag imposed on the instrument in order to maximize the tactile feedback. That objective typically conflicts with the ability of the device to form an effective seal about the instrument. It also is among the general objects of the invention to provide an improved hemostatic valve in which the drag imposed on the inserted instrument may be reduced.